As magnetic recording densities progressively increase and track widths correspondingly decrease, magnetic bit cells are of such size that the use of hard nonmagnetic particles, which have been commonly used to improve wear resistance of disk coatings, must be minimized. Further, as new magnetic particles such as cobalt surface diffused or cobalt modified gamma iron oxide magnetic particles are developed to meet density requirements, high matrix curing temperatures have been found to impair the particle magnetic properties. This degradation may occur as a consequence of cobalt diffusion and reduction of magnetic properties. Also, the coating material must be capable of forming a very thin coating with a smooth surface that will allow a transducer carrying slider assembly to fly only a few millionths of an inch above the surface. It is known in the state of the art that the thinner the coating the better the magnetic performance. A coating thickness of less than 40 microinches is commonly required by high performance rigid magnetic media. To achieve the above property, the coating material must be formed of stable of magnetic particles uniformly dispersed in a binder free from resin gel (insoluble resins). Any gel particles that exceed 1 micron must be minimized. These properties are in addition to the commonly required characteristics of magnetic disk coatings such as being adaptable to normal coating techniques, capable of withstanding repeated head loadings, able to achieve high orientation ratios and capable of good abrasion resistance, impact resistance and corrosion resistance.
The prior art includes numerous patents showing different compositions for recording coatings. U.S. Pat. No. 3,058,844 discloses a magnetic coating composition containing epoxy and phenolic resins, an acid anhydride catalyst, polyvinyl methyl ether and ferromagnetic particles. The use of an acid catalyst in this patent promotes a low cure temperature, but also causes the coating to be unstable and resin gel particles to form as a result of the unstable interation of the catalyst with epoxy at room temperature. This result is not acceptable for a thin, high performance magnetic coating. U.S. Pat. No. 3,843,404 discloses an epoxy/phenolic base magnetic coating having alumina particles dispersed therein to increase the coating durability. The use of hard nonmagnetic alumina particles to improve the durability of the coating, increases magnetic defects, and further, limits the magnetic recording density. U.S. Pat. No. 4,076,890 shows a magnetic coating composition employing resins, ferromagnetic particles and a silane coupling agent. U.S. Pat. No. 4,397,751 discloses an epoxy/phenolic base magnetic coating having a titanate coupling agent as a dispersant. Both patents describe the improvement of magnetic particle dispersion, yet require a high cure temperature to achieve good coating properties. The high temperature cure condition is not compatible with advanced cobalt modified magnetic particles.